1. Field of the Invention
This invention relates to a re-imaging optical system for reducing an image formed by an objective lens, and in particular to a re-imaging optical system suitable for use in the image pickup lens or the like of a television camera used in the gathering of news data (ENG) or the field of program production (EFP).
2. Related Background Art
An an optical system added to an objective lens, there is known a so-called relay optical system for moving an image formed by the objective lens to a desired position and re-imaging it thereat, a converter for changing the combined focal length of a photo-taking lens, or an extender optical system for changing the combined focal length of a zoom lens.
An ENG or EFP camera requires a three-color resolving prism system to be disposed in order to obtain a color image and therefore requires a sufficient back focal length to be secured. Also, in order to prevent the color shading which adversely affects an image by variation of the reflection and transmission characteristics of light entering the dichroic film in the three-color resolving prism, it is necessary to set the exit pupil of the objective lens sufficiently distantly.
Accordingly, to divert a lens for a 35 mm single-lens reflex camera to the ENG or EFP camera, it is necessary to reduce the picture plane by a rear converter while maintaining a sufficient back focal length for disposing the three-color resolving prism, and while providing a desired angle of view and quality of image.
However, the back focal length of a wide angle lens for a 35 mm single-lens reflex camera and of a fish-eye lens is generally of the order of 40 mm and in addition, there is the problem that the back focal length is shortened considerably to reduce the picture plane by the rear converter. Thus, it has been difficult to reduce the image in order to secure the angle of view by the rear converter in which a lens is disposed within a usual back focal length, and to secure a sufficient back focal length and a sufficiently distant exit pupil.
Also, where a re-imaging system is adopted, the image formed thereby is an image resulting from inverting the usual image, and this gives rise to the problem that the finder image is inverted.